Tomato Plant Leaves Turning Brown and Curling? Reasons and How to Fix

Are your tomato plants’ leaves turning brown and curling? As a gardener, it can be quite frustrating to realize things are not going well in your garden as anticipated. Let’s look at what causes this problem and how to fix it.

Brown and curling leaves in tomatoes can result from too little or excessive water, extreme temperatures, nutritional deficiencies, excess nitrogen, insect infestation, viral infections, or due to transplant shock.

However, in some cases, leaf roll can result from a physiological response. It is believed that the plant can roll the leaves in a self-defense mechanism either from the sun or other harsh conditions.

Why are tomato plant leaves turning brown and curling?

Tomato plant leaves can discolor and curl due for a number of reasons including the following:

1. Under or over-watering

Tomato plants require adequate water especially when flowering and fruiting. The general health of your tomato plants is determined by the way you water them. Both inadequate and excessive water in the soil can stress out tomato plants.

Too little water causes stunted growth and also the leaves may curl inwards. On the other hand, excess water can harbor diseases that may also cause brown spots and curling of the leaves. Tomatoes splitting on the vine is also a problem of too much water in the soil.

2. Dry weather or excessive heat

Tomato plants require warm summer weather to grow healthy. However, when the temperature rises above 85 degrees Fahrenheit for a consistent period of time, the tomato plant may start to experience heat stress. 

Excess heat increases the rate of transpiration. During this period, the plant loses more water through the leaves. To prevent further water loss, the tomato plant will curl the leaves inwards. It helps to minimize the surface area exposed to transpiration.

3. Mineral deficiency

Mineral deficiency in tomatoes can also be characterized by yellow or brown and curled leaves. Tomato plants are heavy feeders, they require fertilizer after every two weeks. However, you are supposed to go slow on nitrogen especially when the plant is near flowering.

4. Hormone weed killer

Did you notice curled tomato leaves some days after using a weed killer? Tomato plants are highly susceptible to the effects of hormone weed killers. Be sure to store herbicide bottles away from your tomatoes. Storing herbicide bottles within a greenhouse can affect your tomatoes, especially in warm conditions.

5. Too much wind

Too much or excess wind can be detrimental to your tomato plants. If your tomato plants are not properly staked or supported, they may fall onto the ground or twist and hence causing the leaves to curl. Some of the leaves may turn brown before falling off from the plant.

6. Cold temperatures

Tomato plants do well in the summer season when the temperatures are warm. However, when winter sets in, the temperature drops drastically. This will have negative effects on your tomato plants. The plants will not be able to process enough carbohydrates and hence the leaves will start to curl upwards.

7. Viral diseases

Tomato leaves can also curl due to a viral infection. Apart from the upward curling of the leaves, the plant may also exhibit other symptoms like stunted growth, yellowing of the leaves, brown spots on leaves, and wilting. The flowers may also fail to develop or they may fall off without developing into fruits.

8. Transplant shock

If you notice a leaf curl in a newly transplanted tomato then it may be due to transplant shock. A slight disturbance on a young tomato plant can damage the roots. The plant may exhibit various symptoms like yellow leaves, wilting, and leaf curls. However, the plant normally recovers from this shock within the first two weeks after transplanting.

9. Excess nitrogen

When a tomato plant is young, it is recommended to use a balanced fertilizer containing nitrogen, phosphorus, and potassium. However, you are supposed to reduce the use of nitrogen as the plant approaches flowering.

Too much nitrogen can cause the leaves to become curly. Also, excessive nitrogen causes the foliage to grow at the expense of the fruits. The stems and leaves grow broad with little or small fruit.

10. Pests damage

Insect infestation can also cause the leaves to curl inwards. Spider mites and aphids are the common insects that are found on the underside surface of tomato leaves. These insect pests can also cause the leaves to become brown and scorched.

Other insects like cutworms that are found in the soil can attack the roots of your plants. They feed on the roots causing the plant to have stunted growth, yellow leaves, wilting, or even death of the whole plant.

11.  Excessive pruning

Excessive pruning can also cause a tomato plant to become stressed. The leaves play a very important role in making the carbohydrates that the plant uses. Therefore, when you remove too many of them can cause the plant to struggle in making its own food.

Over-pruning a young plant that has not established itself can lead to stress that may trigger leaf curling and other symptoms like stunted growth, yellow leaves, and poor-quality yields.

How to treat tomato leaf curl

Tomato plants require a lot of care and maintenance for them to grow healthy and produce high yields. The key to managing tomato leaf curls is prevention. It is important to:

• Protect your tomato plants from excess heat by installing a shade cloth over your plants when the temperatures are above 85 degrees Fahrenheit. Be sure to expose them fully to the morning and afternoon sunlight.
• Provide your plants with adequate water. Water early in the morning before the sun rises. Avoid watering the foliage. Direct the water to the base of the plant near the roots. Once you adopt a correct watering schedule, the tomato leaves should be able to return to normal.
• Curled leaves due to mineral deficiency can be fixed by adding fresh compost manure around your tomato plants. Alternatively, you can use an all-purpose fertilizer in order to correct the effects. Conducting a simple soil test can also help you to determine the exact nutrient that is lacking in the soil.
• If the leaf curl is due to a viral infection, uproot the affected plant and burn it to prevent further transmission to other nearby plants.
• Plant pest and disease resistance tomato varieties to prevent cases of leaf curl and other problems.
• Keep your garden free from weeds. Some weeds attract pests and diseases that will eventually affect your tomatoes.
• Keep all herbicides and other weed killers away from the garden or greenhouse. You should also ensure mulch or compost manure is free from herbicides before using them in your garden.
• Keep the plant off the soil by applying mulch and staking early. It helps to improve air circulation around the plant as well as preventing fungal and viral infections.
• Tomato leaf curling due to too much wind can be prevented by early staking. Unsupported tomato plants are likely to twist and form curly leaves when blown by the wind.

Can tomato plants recover from leaf curl?

Environmental factors are the major cause of leaf curls in tomatoes. When your plants develop this problem, it simply means that they are exposed to too much sun, too much cold, excess wind, or inadequate moisture in the soil.

Leaf curl due to environmental issues is not a major cause for an alarm. As soon as the environmental conditions change, the leaves will be able to open back to their normal. This also applies to mineral deficiency, when the underlying deficiency is solved, the plant will be able to grow back to normal leaves.

If the leaf curl is not solved by treatment or preventive measures, then your plants may be suffering from a viral infection. A viral infection is very dangerous to plants. The spread of the virus is quite fast and commonly kills the plant within a short period of time.

Once you realize that your tomato plant is suffering from a viral infection, be sure to uproot it and burn or bury it. It helps to prevent the infection from spreading to other healthy plants.

Final Thoughts

Tomato plant leaf curl is unlikely to cause low yields as long as the vines are in a healthy condition. If you plant a good quality tomato variety that is pest and disease resistance, optimize the growing conditions, and apply fertilizer as recommended, you can prevent leaf rolling and produce high yields in tomatoes.

References

Tomato Disease Identification Key by Affected Plant Part – Cornell University

Recognizing Tomato Problems – Colorado State University

Vegetable IPM Advisory – Utah State University Extension

Common Diseases of Tomatoes By Rebecca A. Melanson, PhD, Assistant Extension Professor, Plant Pathology, Central Mississippi Research and Extension Center.